<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
      /*   利用浮动，flex,绝对定位 */
        .outer {
            display: flex;
           height: 100px;
        }

        .left {
            width: 200px;
            height: 100%;
            background-color: aqua;
        }

        .right {
            flex: 1;
            height: 100%;
            background-color: aquamarine;
        }
    </style>
</head>
<body>
    <div class="outer">
        <div class="left">左侧</div>
        <div class="right">右侧</div>
    </div>
</body>
</html>